Plasma-Sprayed NiCrCuMoB High Entropy Alloy Coating with low oxide content enabled by Boron Alloyed Powder

Plasma-sprayed metal coatings are used to protect metals from corrosion and erosion. Due to the unique properties of high entropy alloys (HEAs), their thermal spray coatings have been intensively investigated. However, due to severe in-flight oxidation and high oxide inclusions, their properties are generally lower compared with their bulk counterparts. In this study, NiCrCuMo HEA powders containing boron were designed to deposit the HEA coatings with oxide-free molten droplets by atmospheric plasma spraying. The in-flight in-situ deoxidizing effect through boron was examined through the collected HEA particles passing through plasma jet. The isolated splats were deposited on both the polished stainless-steel and NiCr substrates for examining their bonding to substrate. The coating microstructure and mechanical and electrochemical properties were investigated. Results show that in-flight oxidation of molten particles is effectively suppressed and oxide-free HEA particles are achieved. The coatings present a dense microstructure and adhesion higher than 65MPa due to adhesive failure. The electrochemical test reveals the promising corrosion resistance of the coatings. It is confirmed that through full utilization of boron deoxidizing effect the bulk-like HEA coatings of metallurgical bonding and low oxide content can be achieved.